a 737 is a 737 is a 737...
No it isn't. In JAA land the 737-100/200 is separate from the 300/900, and the only way to 'convert' is through a new type rating. I know this, as I have a 200 rating from a few years back, not paid for by me, which is now useless unless I want to fly in some rathole like Iraq or Saudi. Jet time as such is not that useful unless it is on a worthwhile type (again from experience), so I would save your money and politely decline, otherwise you will end up buying another rating in the future and be more a hobby pilot than someone who actually makes a living from it.